1. Fish Production, Growth, Survival rate and Food Conversion Rate (FCR)
Production of fish after six months growout period are shown in Table 2. The average production of fish (kg per ha) in low density of prawn (L.D) were as follow; 864, 392, 259 and 782 respectively for common carp (C.C), giant gourami (G.G), bighead carp (B.C) and silver carp (S.C). While in high density of prawn (H.D) the production of C.C, G.G, B.C and S.C were 796, 280, 267 and 784 respectively. These production from each species between L.D and H.D were not significant (P < 0.05). The survival rate of C.C was the highest (92%), followed by B.C (83% and 93%), S.C (89% and 80%) and G.G (76% and 73%). Both survival rate in the bracket were in L.D and H.D. There were no significant difference (P < 0.05) between the survival rate in L.D and H.D for each species of fish.
The body weight and length presented in Table 3 and Table 4. It shows that the weight and length increament of C.C was the highest either in L.D or in H.D compared with other species. In Figure 1 the pattern of average of body weight was almost similar both in L.D and H.D, and this was also occurred in the pattern of average of body length (Fig. 2). From body weight and length increament (Table 3 and 4) shows that S.C have had the lowest increament both in weight and length, especially after third sampling (7.44 g and 17.99 g in body weight; 0.63 cm and 0.25 cm in body length). Followed by B.C and G.G. From statistical analysis it shows that both weight and length increament at each sampling were not significant (P < 0.05). Except for body weight increament of G.G and S.C at first and second sampling respectively. And the body weight of C.C at second sampling. It was more clear, however, if we notice the percentage weight gained (% per day) as it is shown in Table 5 and Fig. 3. The percentage weight gained of C.C increased within first sampling up to third sampling (111.6 – 802.0% (L.D); 71.0 – 819.0% (H.D)), afterward it decreased at the rate of 661.8% and 757% in L.D and H.D respectively. As for S.C, it decreased starting from second sampling up to fourth sampling (102.4 – 11.6% (L.D); 104.4 – 28.1% (H.D)). The B.C, even it decreased starting from first sampling up to fourth sampling (194.0 – 84.1% (L.D); 185.0 – 58.7% (H.D)). Only the percentage weight gained of G.G which increased starting from first sampling up to fourth sampling (50.9 – 211.8% (L.D); 30.7 – 197.1% (H.D)). The percentage weight gained of each species between L.D and H.D was not significant (P < 0.05) in each sampling time, except for G.G in first sampling and S.C in second sampling.
The food conversion rate (FCR) of fish in L.D and H.D were 0.85 and 1.12 respectively. Besides pellets, fish and prawn were fed in small amount comparatively with chopped fish, broken rice and corn in case of pellets were not available (Table 6). In addition the shopped fish consumption was converted into dry matter (± 25%) prior to FCR calculation.
2. Prawn Production, Survival rate, and FCR
Prawn production (kg per ha) and survival rate (%) after seven months growout period between L.D and H.D were not significant (P < 0.05). The average production in L.D and in H.D were 721 and 908 respectively. The survival rate range from 49.1 – 61.1%, except in P12 (Table 2) which was up to 95%. The FCR of prawn was about 2.5. It was estimated from the previous experiment on prawn monoculture (Boonyaratpalin, 1986, pers. comm).
3. Prawn Yield Characteristics
Prawn yield (kg per pond) from each partial harvest between L.D and H.D were not significant (P < 0.05), even in total yield (Table 7). At partial harvests, the yields in L.D were 96 and 35, while in H.D were 107 and 77. Two months later, at second partial harvests, the yields were recorded as follow 42 and 99 in L.D and 100 and 121 in H.D. Such a big difference in yield was occurred in L.D replicates after third partial harvests (49 and 159), while at H.D replicates were 120 and 165 respectively. This resulting a big difference in total yield in L.D as well (187 and 293.7). Total yield in H.D were 328 and 383 respectively. The yield from each category at each replicate varied at three times partial harvests as shown in Fig. 4 and 5. At the end of culturing period, there were some prawns remained under marketable (U.M) size, which the U.M prawn yields in between two replicates in L.D were quite different (49 and 159), while in H.D it were 120 and 165 respectively (Table 7).
The average weight (g per prawn) or the marketable males from each category was more varied compared with that of marketable females (Fig. 6 and 7) both in L.D and H.D at each harvesting. The average weight of males no. 1–3 were ranged from 32– 119 g, while long claws (L.CO varied from 83–140 g, and 36–64 g for soft shell category. The range of the average weight of females were 30–59 g and 26–46 g for females with eggs and females without eggs respectively. As for under marketable sized prawn (U.M), the average weight ranged from 14–17 g (Table 7).
Prawn numbers which were harvested partially are shown in Table 8. There were no significant difference (P < 0.05) in prawn numbers between L.D and H.D at each partial harvest or even in total numbers. The prawn numbers harvested in L.D were quite different in between its replicates, especially in third partial harvest (1,595 and 5,233). As a result, the total number of prawns in L.D were almost double in between replicates, which were 3,911 and 7,846 respectively (Table 8). The prawn numbers harvested in H.D were not so much different in between replicates compared with in L.D, except in third harvest which was almost double (3,985 and 6,436), however, the total number of prawns were comparatively closed in between replicates, which were 9,261 and 1,156 respectively (Table 8).
Percentage in weight (%) of female prawns at first and second partial harvests were not significant, but there were a significant difference at third harvest (P > 0.05) and very significant (P > 0.01) at the total yield. Data presented in Table 7 shows that the percentage in weight of females in both L.D and H.D were higher that of males at third harvest and at total yield. The percentage in L.D, however, was lower than that in H.D. In other words there is a positive relationship between the percentage in weight of females and the prawn numbers of stocking (r2 = 0.99).
Percentage in number (%) of female prawns at first, second and third partial harvests were not significant (P < 0.05), but there was a significant difference at total prawn numbers (P > 0.05) between L.D and H.D. As in percentage in weight, the percentage in numbers of female prawns was higher than that of males, and also the percentage in number of female prawns in L.D was lower than that in H.D (Table 8). The positive relationshop was occurred as well between the percentage in number of females and the prawn number of stocking (r2 = 0.85).
The marketable and unmarketable sized prawns in weight (kg) were not significant (P < 0.05) between L.D and H.D, however, there was significant difference (P > 0.05) in number of marketable sized prawns. The percentage in weight (2) of marketable sized prawns in L.D and H.D were 69.9 and 73.2 respectively, while the percentage in number (%) were 87.6 and 87.8 respectively (Table 9).
4. Water quality and Biological Parameters
During culturing period, water quality and biological parameters were monitored namely water temperature (T), dissolved oxygen (DO), pH, ammonia (NH3), hydrogen supfide (H2S), hardness, alkalinity as well as turbidity. As for biological parameters are as follows: stomach content, benthos, chlorophyll and organic matters. Water Temperature and Dissolved Oxygen
Temperature (°C) in the morning both in L.D and H.D almost the same, ranging from 24.81 – 31.50°C (28.60 ± 1.74), while in the afternoon it ranging from 25.21 ± 34.88°C (31.73 ± 2.07). Temperature between surface and bottom in the morning were similar and also in the afternoon except in January, whereas the difference up to 3°C within one week. Dissolved oxygen (ppm) in both surface and bottom in L.D and higher compared with that in H.D either in the morning or in the afternoon. The range of DO in both surface and bottom at morning monitoring amounted from 2.65 – 9.15 (4.44 ± 1.42) and 2.10 – 5.33 (3.53 ±0.96), compared with that was occured in H.D ranging from 1.95 – 6.68 (4.00 ± 1.30) and 1.45 – 6.08 (3.36 ± 1.19) respectively in surface and bottom. The DO fluctuation of L.D and H.D in the morning were less compared with that occured in the afternoon monitoring (Appendix 1 and 2), whereas the mean DO in the morning ranged from 3.36 – 4.44, while mean DO in the afternoon ranged from 5.46 – 8.73. The DO diurnal which was conducted during a period of January-May (Appendix 3, 4 and 5) shows that the peak of DO level occured at 2–4 p.m. in both surface and bottom while the lowest occured at 6 a.m. Also during this period there was a decreasing of DO level. As comparison, the lowest DO level in both L.D. and H.D in January was about 6.0 to 6.5 while in April declined to 2.7–3.6 and in May it declined into 2.3–3.1.
Ammonia and pH
In Appendix 6 shows that the concentration of ammonia (ug/1) initially was about 100–150, later on it decreased until April, afterward increasing up to reach the peak on May to June at the level of 545–648 (L.D) and 305–409 (H.D). In June to July, however, it decreased again in both L.D and H.D amounted to only 8–17. (Appendix 6). The pH fluctuation between surface and bottom in both LD and H.D were not so much different, except on May (22nd week) which within one week the pH dropped from 7.99 to 7.11 in L.D and from 7.72 to 6.86 in H.D (Appendix 7). The mean pH ranged from 7.82 to 8.02 ( ± 0.33) in both L.D and H.D.
Hardness, Alkalinity and Hydrogen Sulfide
Hardness (mg/l of CaCO3 eq) fluctuated starting from mid December until mid March with the range of 137–360 in both L.D and H.D Afterward it was more stabil until July ranging from 132–165. Alkalinity (mg/l) more less stabil compared with hardness, which ranging from 50–133 (Appendix 8). Monthly monitoring of hydrogen sulfide (mg/l) shows that there was a decreasing starting from January until June. Initially it was about 1.42–1.72 (in L.D) and 1.12–1.52 (in H.D) afterwards it was dropped into a level of 0.64–0.42 (in L.D) and 0.35 – 0.6 (in H.D). The difference between in surface and bottom was not so much, except on May whereas amounted to 0.75 and 1.49 (in L.D) and 0.56 and 1.21 (in H.D) respectively occured in bottom and surface (Appendix 9)
Turbidity
In general, during culture period turbidity (cm) increased (pond water more turbid) in both L.D and H.D, up to only 6–7 cm. Starting from 23–29 cm. (Appendix 10).
Stomach Content
By means of a mean bulk index (M.B.I), stomach content of fish and prawn were conducted. The results (Appendix 11 and 12) shows that both fish and prawn mainly utilized artificial feeds (pellet) as their food. Only in certain case, such as giant gouramy which sometimes utilized aquatic plant as a main input, especially it was more obvious at second sampling (Appendix 12). Others important items were recorded such as zooplankton and phytoplankton for silver carp and bighead carp, benthos for common carp and prawns.
Benthos
Monthly data of benthos (individuals per sq.m) existed in ponds is shown in Appendix 13. There was a big difference between existed in L.D and H.D during early January until late February, whereas the peak was reached in H.D at amount of 2464, while in L.D only 657. (Appendix 13). Starting from late February until late May, however, the benthos existed in both L.D and H.D were moreless the same.
Chlorophyll a
Biweekly data of chlorophyll a (ug/l) is presented in Appendix 14. The chlorophyll a fluctuation between L.D and H.D was similar. Starting from only 30 in mid December increased up to 104 (L.D) and 126 (H.D), afterward it decreased and flucturated at the range of 51–129 until mid June, however, it increased again up to a level of 199 (L.D) and 165 (H.D).
Organic matter
Monthly measurement of organic matter (g/128 sq.cm) in both with and without cover in L.D and H.D were almost in similar pattern, which were always increasing begin from January until June (Appendix 15). The amount of organic matter collected in a container without cover was less compared with that without cover.
5. Economical Analysis
Table 11 shows the variation in market price (Baht per kg) for different categories based on March until July 1986 prices. The price of female prawns and soft shell prawns were not so much different, however, the price difference (margin) of males in grade 1, 2 and 3 ranged from 10 to 20 baht.
The comparison of yields and revenues of prawn between in L.D and in H.D at each partial harvest are shown in Table 12. Both yield and revenues increased from first harvest up to third harvest, where in H.D both yield and revenues higher than that in L.D (Fig. 10). Total yield and revenues of prawn in L.D and H.D were comprised of 481.3 kg; 45,149 baht and 711.1 kg; 64,447 baht respectively (Table 13). While the yield and revenues of fish are as follows 1,318.5 kg; 21,523 baht in L.D and 1,222 kg; 19,225 baht in H.D. So the total revenues of prawn and fish in L.D and H.D amounted to 66,672 baht and 81,752 baht respectively (Table 13).
In Table 15, shows the comparison of the operating costs between L.D and H.D during 7 months growout period. The total operating costs in L.D and H.D amounted to 45,022 baht and 60,372 baht respectively. The fixed costs of both were the same about 3,730 baht or 8.3% and 6.2% of total operating costs respectively for L.D and H.D. The variable costs in L.D comprised 41,292 baht or 91.7% of total operating costs, while in H.D was about 56,642 baht or 93.8% of total operating costs. Feed made up 48.2% and 44% of total variable costs respectively for L.D and H.D, followed by fish fingerling (20.9%) in L.D and Prawn juveniles (26.7%) in H.D; Prawn juveniles (12.5%) in L.D and Fish fingerling (15.6%) in H.D; Labor comprised 5.8% and 4.3% in L.D and H.D respectively. Other expenses of each item was less than 3%. The production cost of both prawn and fish (baht per kg) was 25 (in L.D) and 31 (in H.D), with the rate of return on operating cost (%) comprised 48 and 38 (Table 16). In Table 15 also shows that the profit (net revenues) per pond in L.D was lower than that in H.D (21,650 baht; 23,300 baht), however the profit per kg was the same which amounted to 12 baht per kg.
